Passive frequency multiplexer

ABSTRACT

A passive frequency multiplexer includes a beam forming network lens including a plurality of input terminals and a plurality of output terminals; a transmission line for transmitting a signal to the beam forming lens; and a plurality of couplers arranged in series along the transmission line, each of the plurality of couplers comprising an input terminal, an output terminal, and a coupled output terminal, each of the coupled output terminals of the plurality of couplers being coupled to a respective one of the input terminals of the beam forming network lens.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional of U.S. patent application Ser. No.15/133,060, filed Apr. 19, 2016, entitled “PASSIVE FREQUENCYMULTIPLEXER”, the entire content of which is incorporated herein byreference.

BACKGROUND 1. Field

Example embodiments of the present invention relate to a passivefrequency multiplexer for passive RF signal processing.

2. Description of the Related Art

Frequency domain information is typically acquired from time domainsignals via sampling, high-speed digitization, and digital signalprocessing. This process consumes a large amount of power and requires ahigh volume of processors.

SUMMARY

Embodiments of the present invention are capable of converting timedomain signals to frequency domain signals in real time using passive RFcomponents. Embodiments of the present invention include a beam formingnetwork lens connected to RF couplers located in series along atransmission line. According to embodiments of the present invention, aninput signal is provided on the transmission line, and each RF couplercouples a portion of the input signal to a respective input on the beamforming network lens. Using planar wave construction and deconstruction,the beam forming network lens forms sums and nulls at the beam taps(outputs) of the beam forming network lens to split the input signalinto frequency groups that can be directly sampled at the beam taps.

Embodiments of the present invention include a passive frequencymultiplexer including a beam forming network lens comprising a pluralityof input terminals and a plurality of output terminals; a transmissionline for transmitting a signal to the beam forming lens; and a pluralityof couplers arranged in series along the transmission line, each of theplurality of couplers comprising an input terminal, an output terminal,and a coupled output terminal, each of the coupled output terminals ofthe plurality of couplers being coupled to a respective one of the inputterminals of the beam forming network lens.

The beam forming network lens may be a time-delay beam forming networklens.

The beam forming network lens may be a Rotman lens.

The beam forming network lens may be a phase-shift beam forming networklens.

The plurality of couplers may include tuning couplers.

The plurality of couplers may include serial beam spoilers.

The plurality of couplers may include amplitude tapers.

The beam forming network lens may include a plurality of beam formingnetwork lenses.

Spacing between adjacent ones of the plurality of couplers may be thesame for each adjacent pair of the plurality of couplers.

Embodiments of the present invention include a passive frequencymultiplexer including a Rotman lens including a plurality of steer portsand a plurality of beam ports; a transmission line for transmitting asignal to the Rotman lens; and a plurality of couplers arranged inseries along the transmission line, each of the plurality of couplersincluding an input terminal, an output terminal, and a coupled outputterminal, each of the coupled output terminals being coupled to arespective one of the steer ports of the Rotman lens, a spacing betweenadjacent ones of the plurality of couplers being the same for eachadjacent pair of the plurality of couplers.

The plurality of couplers may include tuning couplers.

The plurality of couplers may include serial beam spoilers.

The plurality of couplers may include amplitude tapers.

The Rotman lens may include a plurality of Rotman lenses.

Embodiments of the present invention may include a method of passivelyconverting a time domain signal to a frequency domain signal in realtime, the method including receiving the time domain signal via atransmission line; coupling respective portions of the time domainsignal to input terminals of a beam forming network lens via a pluralityof couplers; reading an output signal at an output terminal of the beamforming network lens; applying a simple rectification to the outputsignal to acquire a rectified output signal; and converting therectified output signal from analog to digital using an analog todigital converter to acquire the frequency domain signal.

The beam forming network lens may be a Rotman lens.

The plurality of couplers may include tuning couplers.

The plurality of couplers may include serial beam spoilers.

The plurality of couplers may include amplitude tapers.

The beam forming network lens may include a plurality of beam formingnetwork lenses.

BRIEF DESCRIPTION OF THE DRAWINGS

Illustrative, non-limiting example embodiments will be more clearlyunderstood from the following detailed description taken in conjunctionwith the accompanying drawings.

FIG. 1 is a circuit diagram illustrating a passive frequency multiplexeraccording to an embodiment of the present invention.

FIG. 2 is a circuit diagram illustrating a passive frequency multiplexerutilizing a Rotman lens according to an embodiment of the presentinvention.

FIG. 3 illustrates frequency domain signals read out from threerepresentative beam ports of a Rotman lens with seventeen beam ports andeight steer ports according to a model of an embodiment of the presentinvention.

FIG. 4 illustrates frequency domain signals read out from threerepresentative beam ports of a Rotman lens with seventeen beam ports andsixteen steer ports according to a model of an embodiment of the presentinvention.

FIG. 5 illustrates output of first to ninth frequency bins according toa model of two concurrent pulses with different frequencies and pulsewidths but the same pulse repetition interval (PRI).

FIG. 6 illustrates a frequency response of first, fifth, and ninth beamports 224 with a normal S-parameter sweep using the serial feed and theRotman lens used in the model of FIG. 5.

FIG. 7 illustrates experimental frequency domain signals read out fromthree representative beam ports of a Rotman lens with eighteen beamports and eighteen steer ports according to an embodiment of the presentinvention.

DETAILED DESCRIPTION

The example embodiments are described more fully hereinafter withreference to the accompanying drawings. Like reference numerals refer tolike elements or components throughout.

Embodiments of the present invention are capable of converting timedomain signals to frequency domain signals in real time using passive RFcomponents. Embodiments of the present invention include a beam formingnetwork lens connected to RF couplers located in series along atransmission line. According to embodiments of the present invention, aninput signal is provided on the transmission line, and each RF couplercouples a portion of the input signal to a respective input on the beamforming network lens. Using planar wave construction and deconstruction,the beam forming network lens forms sums and nulls at the beam taps(outputs) of the beam forming network lens to split the input signalinto frequency groups that can be directly sampled at the beam taps.

FIG. 1 is a circuit diagram illustrating a passive frequency multiplexeraccording to an embodiment of the present invention and FIG. 2 is acircuit diagram illustrating a passive frequency multiplexer using aRotman lens according to an embodiment of the present invention.

Referring to FIG. 1, a passive multiplexer 100 includes a beam formingnetwork lens 120, a transmission line 140, and a plurality of couplers160 (e.g., RF couplers 160). The beam forming network lens 120 includesbeam forming network lens input terminals 122 and beam forming networklens output terminals 124. The couplers 160 include input terminals 162,output terminals 164, and coupled output terminals 166.

The couplers 160 are connected in series along the transmission line140. Other than the first coupler 160, each input terminal 162 of thecouplers 160 is connected to an output terminal 164 of a previouscoupler 160. The coupled output terminals 166 of each coupler 160 isconnected to a beam forming network lens input terminal 122 of the beamforming network lens 120.

A length of the transmission line 140 has n couplers 160 placed along it(n is an integer and n=8 in FIGS. 1 and 2). The spacing betweenneighboring couplers 160 may all be the same, but the present inventionis not limited thereto. In some embodiments, the spacing betweenneighboring couplers 160 is a multiple of a characteristic wavelength λof the signal (e.g., λ, λ/2, 2λ, etc.). The characteristic wavelength λis a wavelength at the middle of the frequency band of interest.

While the example embodiments of the present inventions use couplers,the present invention is not limited thereto. For example, powerdividers (reactive tees, Wilkinson, etc.) may be used.

The n couplers 160 are respectively connected to n beam forming networklens input terminals 122 of the beam forming network lens 120 such thatamplitude and phase are normalized and equal. There are m beam formingnetwork lens output terminals 124 of the beam forming network lens 120that act as m frequency bins (m is an integer and m=9 in FIGS. 1 and 2).

A signal is applied to the transmission line 140 (IN). The signal passesthrough the couplers 160 and a portion of the signal is coupled to thebeam forming network lens input terminals 122 by the couplers 160 viathe coupled output terminals 166. An output can be read out at the beamforming network lens output terminals 124 (OUT).

Applying simple rectification to the readout of the m beam formingnetwork lens output terminals 124 and inputting the result to adigitizer (analog to digital converter) will sample amplitude of thefrequency domain directly. Planar waves will construct and deconstructat the beam forming network lens to form sums and nulls at beam formingnetwork lens output terminals 124 such that a frequency at thecharacteristic wavelength λ will appear like an m-point sync functionwith a peak at the center, a lower frequency will show up as an m-pointsync function with a peak at the left, and a higher frequency will showup as an m-point sync function with a peak to the right.

Embodiments of the present invention can be implemented as a singledevice. For example, the plurality of couplers 160 can be integratedinto the beam forming network lens 120, such that the integrated devicehas a single input terminal 122 and multiple output terminals 124 andthere would be no need for additional external couplers 160.

Referring to FIG. 2, in some embodiments of the present invention, apassive multiplexer 200 includes a Rotman lens 220. When the beamforming network lens 120 is a Rotman lens 220, the beam forming networklens input terminals 122 may be steer ports 222 (or array ports 222) andthe beam forming network lens output terminals 124 may be beam ports 224(or beam taps 224).

In embodiments of the present invention input ports may be referred toas array ports on a conventional lens, and output ports may be referredto as the beam ports on a conventional lens. Further, according toembodiments of the present invention, output ports may be frequencybins.

Signals entering the Rotman lens via the steer ports 222 travel varyingdistances to reach the beam ports 224. As represented by the dashedlines, signals travelling the varying distances arrive at one of thebeam ports 224 and, by construction and deconstruction, form sums andnulls to create the signal that is read out at the beam port 224.

While FIG. 2 shows the beam forming network lens 120 as a Rotman lens220, the present invention is not limited thereto. Further, the Rotmanlens 220 is an example of a time-delay beam forming network lens but thepresent invention is not limited thereto and a phase-shift beam formingnetwork lens (e.g., a Butler matrix lens) may be used. For example, thebeam forming network lens 120 may be implemented as a Rotman lens 220, aRotman-Archer lens, a Butler matrix lens, etc.

While the embodiments provided in FIGS. 1 and 2 show eight couplers 160and show that the beam forming network lens 120 has eight beam formingnetwork lens input terminals 122 and nine beam forming network lensoutput terminals 124, the present invention is not limited thereto andembodiments of the present invention may include any number of couplers160 and the beam forming network lens 120 may have any number of beamforming network lens input terminals 122 and beam forming network lensoutput terminals 124. Further, embodiments may include a differentnumber of couplers 160 and beam forming network lens input terminals122.

In some embodiments, the number of couplers 160, beam forming networklens input terminals 122, and beam forming network lens output terminals124, as well as the degree of coupling of phase shift of the couplers160, can be varied and optimized to tune for different sample sizes andfrequency fidelity as desired for the specific application. Further,couplers 160 may be tuning couplers or specialized beam formingcouplers.

Further, the beam forming network lens 120 (e.g., the Rotman lens 220)may be physically warped to normalize to frequency.

In other embodiments, serial beam spoils, such as a delta beam, may bebuilt into the n coupler 160 such that all or a portion (e.g., half) ofthe couplers could have a 180° phase shift built into the couplers 160,such that a delta beam (rather than the sync function sum beam) isproduced on the m beam forming network lens output terminals 124.Further, special serial beam spoils and amplitude tapers (e.g., Taylorseries tapers) can be implemented on the couplers 160 to sharpen beamsand reduce sidelobe content. A grating lobe effect may be used tocollect harmonic data.

In yet another embodiment, there may be multiple beam forming networklenses. For example the signal carried on transmission line 140 may besampled as a sum beam at beam forming network lens output terminals 124a of a first beam forming network lens 120 a and sampled as a delta beamat beam forming network lens output terminals 124 b of a second beamforming network lens 120 b. The sum and delta beams may be combined(e.g., in mono-pulse radar) to get higher detailed frequency resolution(i.e., more sharply defined frequency resolution).

In another embodiment, precision placement of the m beam forming networklens output terminals 124 (e.g., at precise angles) can be used to getan increased amount of frequency information from a decreased number ofbeam forming network lens output terminals 124.

Embodiments of the present invention allow for instantaneous or nearinstantaneous conversion of time domain signals to frequency domainsignals without the need to perform a Fourier transform and the relatedprocessing. Embodiments of the present invention may be directed toradio frequencies (i.e., “RF”), but the present invention is not limitedthereto. Sizes of devices according to embodiments of the presentinvention may vary depending on the frequencies that the device isdirected towards.

FIG. 3 illustrates frequency domain signals read out from threerepresentative beam ports 224 of a Rotman lens with seventeen beam ports224 and eight steer ports 222 according to a model of an embodiment ofthe present invention and FIG. 4 illustrates frequency domain signalsread out from three representative beam ports 224 of a Rotman lens withseventeen beam ports 224 and sixteen steer ports 222 according to amodel of an embodiment of the present invention.

Some embodiments of the present invention are described as models.Example models may include an Advanced Design System (ADS) transientmodel.

FIG. 3 shows that a simple Rotman lens with eight steer ports 222 with Aspacing between the couplers 160 shows frequency specific signal peaksoccurring at the various beam ports 224. Specifically, the first, ninth,and seventeenth beam ports 224 are illustrated in FIG. 3. FIG. 4 showsthat a simple Rotman lens with sixteen steer ports 222 with A spacingbetween the couplers 160 shows frequency specific signal peaks occurringat the various beam ports 224. Specifically, the first, ninth, andseventeenth beam ports 224 are illustrated in FIG. 4. In comparing FIG.3 and FIG. 4, it can be seen that when the number of steer ports 222increases, the frequency resolution increases, i.e., the beam peaksnarrow.

The model shown in FIGS. 3 and 4 was set up with input frequencies sweptfrom 2 GHz to 10 GHz. In the model, the center frequency (6 GHz) showsup on the center beam port 224 (ninth beam port 224). The extreme beamports 224 (first and seventeenth beam ports 224) define the upper andlower frequencies (8.5 & 4.6 GHz) that can be detected by the modelledRotman lens 220. The upper and lower frequencies are determined by themaximum scan angle of the Rotman lens 220 (35°, in FIGS. 3 and 4).

FIGS. 3 and 4 show an extra peak on the seventeenth beam port 224 at 9.3GHz which shows a 2:1 bandwidth limitation of the serial feed structurein the modelled Rotman lens 220.

At higher frequencies, the peaks get broader and farther apart, makingit more difficult to resolve the actual frequency. The peaks arenarrower and closer together at the lower frequencies, giving betterfrequency resolution.

FIG. 5 illustrates output of first to ninth frequency bins according toa model of two concurrent pulses with different frequencies and pulsewidths but the same pulse repetition interval (PRI). The model wasperformed with an 8×9 Rotman lens set for 4 GHz. The first pulse has afrequency of 3.7 GHz and has a pulse width of 10 μs and the second pulsehas a frequency of 4.25 GHz, a pulse width of 6 μs, and a 1 μs delay.

FIG. 5 illustrates first through ninth frequency bins (e.g., firstthrough ninth beam ports 224). The first bin shows substantially onlythe 3.7 GHz pulse and the ninth bin shows substantially only the 4.25GHz pulse, with each of the bins therebetween showing some of each ofthe pulses. At the center, the fifth bin shows both the 3.7 GHZ and the4.25 GHz pulses.

FIG. 6 illustrates a frequency response of first, fifth, and ninth beamports 224 with a normal S-parameter sweep using the serial feed and theRotman lens used in the model of FIG. 5. The S-parameter sweep is afrequency sweep that computes the S-parameter responses for the circuitunder test (for example in an ADS model). S-parameters are a measure ofreflection and coupling for n-port networks. When the S-parameter sweepis applied to the modelled hardware of FIG. 5, the results are similarto those of FIGS. 3 and 4.

FIG. 7 illustrates experimental frequency domain signals read out fromthree representative beam ports of a Rotman lens with eighteen beamports and eighteen steer ports according to an embodiment of the presentinvention.

The Rotman lens used was designed for 2-18 GHz operation. Nine NARDA™couplers (model 4203) were cascaded as follows (−16 dB, −16 dB, −10 dB,−10 dB, −10 dB, −10 dB, −6 dB, −6 dB, −6 dB) with approximately 3.5″spacing between each coupler. Flex cables of approximately the samelength were used to connect the coupled outputs of the couplers to everyother one of the steer ports of the Rotman lens. The signals weremeasured on the Rotman lens's beam ports as frequency was swept into theserial input port.

Peaks can be seen between about 2 GHz and about 2.5 GHz for thisspecific setup. The specific Rotman lens that was used here was tuned towork better at higher frequencies, and it can be seen in FIG. 7 that thesecond harmonic frequencies (with peaks between about 4 GHz and about 5GHz) have more clearly formed peaks.

It will be understood that, although the terms “first,” “second,”“third,” etc., may be used herein to describe various elements orcomponents, these elements or components should not be limited by theseterms. These terms are used to distinguish one element or component fromanother element or component. Thus, a first element or componentdiscussed below could be termed a second element or component withoutdeparting from the spirit and scope of the present invention.

The terminology used herein is for the purpose of describing particularembodiments and is not intended to be limiting of the present invention.As used herein, the singular forms “a” and “an” are intended to includethe plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprise,”“comprises,” “comprising,” “includes,” “including,” and “include,” whenused in this specification, specify the presence of stated features,integers, steps, operations, elements, and/or components, but do notpreclude the presence or addition of one or more other features,integers, steps, operations, elements, components, and/or groupsthereof. Further, the use of “may” when describing embodiments of thepresent invention refers to “one or more embodiments of the presentinvention.”

It will be understood that when an element or component is referred toas being “connected to,” “coupled to,” “connected with,” or “coupledwith” another element or component, it can be “directly connected to,”“directly coupled to,” “directly connected with,” or “directly coupledwith” the other element or component, or one or more interveningelements or components may be present. Furthermore, “connection,”“connected,” etc., may also refer to “electrical connection,”“electrically connected,” etc., depending on the context in which suchterms are used as would be understood by those skilled in the art. Whenan element or component is referred to as being “directly connected to,”“directly coupled to,” “directly connected with,” or “directly coupledwith” another element or component, there are no intervening elements orcomponents present.

Also, any numerical range recited herein is intended to include allsubranges of the same numerical precision subsumed within the recitedrange. For example, a range of “1.0 to 10.0” or between “1.0 and 10.0”are intended to include all subranges between (and including) therecited minimum value of 1.0 and the recited maximum value of 10.0, thatis, having a minimum value equal to or greater than 1.0 and a maximumvalue equal to or less than 10.0, such as, for example, 2.4 to 7.6. Anymaximum numerical limitation recited herein is intended to include alllower numerical limitations subsumed therein and any minimum numericallimitation recited in this specification is intended to include allhigher numerical limitations subsumed therein. Accordingly, Applicantreserves the right to amend this specification, including the claims, toexpressly recite any sub-range subsumed within the ranges expresslyrecited herein. All such ranges are intended to be inherently describedin this specification such that amending to expressly recite any suchsubranges would comply with the requirements of 35 U.S.C. § 112, firstparagraph, and 35 U.S.C. § 132(a).

Features described in relation to one or more embodiments of the presentinvention are available for use in conjunction with features of otherembodiments of the present invention. For example, features described ina first embodiment may be combined with features described in a secondembodiment to form a third embodiment, even though the third embodimentmay not be specifically described herein.

Although this invention has been described in certain specificembodiments, those skilled in the art will have no difficulty devisingvariations to the described embodiment, which in no way depart from thescope and spirit of the present invention. Furthermore, to those skilledin the various arts, the invention itself herein will suggest solutionsto other tasks and adaptations for other applications. It is theapplicant's intention to cover by claims all such uses of the inventionand those changes and modifications which could be made to theembodiments of the invention herein chosen for the purpose of disclosurewithout departing from the spirit and scope of the invention. Thus, thepresent embodiments of the invention should be considered in allrespects as illustrative and not restrictive, the scope of the inventionto be indicated by the appended claims and their equivalents.

What is claimed is:
 1. A method of passively converting a time domainsignal to a frequency domain signal in real time, the method comprising:receiving the time domain signal via a transmission line; couplingrespective portions of the time domain signal to input terminals of abeam forming network lens via a plurality of couplers; reading an outputsignal at an output terminal of the beam forming network lens; applyinga simple rectification to the output signal to acquire a rectifiedoutput signal; and converting the rectified output signal from analog todigital using an analog to digital converter to acquire the frequencydomain signal.
 2. The method of claim 1, wherein the beam formingnetwork lens is a Rotman lens.
 3. The method of claim 1, wherein theplurality of couplers comprises tuning couplers.
 4. The method of claim1, wherein the plurality of couplers comprises serial beam spoilers. 5.The method of claim 1, wherein the plurality of couplers comprisesamplitude tapers.
 6. The method of claim 1, wherein the beam formingnetwork lens comprises a plurality of beam forming network lenses.